Monolayers of 1-Alkynes on the H-Terminated Si(100) Surface (original) (raw)
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Alkyl Monolayers on Silicon Prepared from 1-Alkenes and Hydrogen-Terminated Silicon
Journal of the American Chemical Society, 1995
High-quality alkyl monolayers on silicon have been prepared from 1-alkenes and hydrogen-terminated Si(11 1). The 1-alkenes form monolayers upon free-radical initiation with diacyl peroxides. Heat also initiates monolayer formation, although monolayers prepared from heated long-chain 1-alkenes are of lower quality than those prepared with free-radical initiation. Even when a high concentration of diacyl peroxide is used to initiate monolayer formation, the 1-alkene is the primary constituent of the monolayer. Alkynes also form monolayers on silicon when initiated by diacyl-peroxides. X-ray reflectivity shows that the monolayer thickness is of molecular dimensions and that the density is close to that of crystalline hydrocarbons (-90%). Infrared spectroscopy shows that the alkyl chains in the monolayers are densely packed. Infrared dichroism shows that the chains are tilted from the surface normal and twisted about their axes. The wetting properties of the monolayers show that they are methyl terminated. After many weeks of air exposure, the silicon substrate under the monolayers is not significantly oxidized. The monolayers are very stable to boiling chloroform, boiling water, boiling acidic and basic solutions, and fluoride and are at least as stable as similar chain-length monolayers prepared from trichlorosilanes on oxidized silicon. We propose that alkyl chains in the monolayers are bound to the silicon substrate through silicon-carbon bonds and compare a proposed mechanism of bond formation to analogous homogeneous reactions.
Molecular Modeling of Alkyl Monolayers on the Si(100)−2 × 1 Surface
Langmuir, 2004
Molecular modeling was used to simulate various surfaces derived from the addition of 1-alkenes and 1-alkynes to SidSi dimers on the Si(100)-2 × 1 surface. The primary aim was to better understand the interactions between adsorbates on the surface and distortions of the underlying silicon crystal due to functionalization. Random addition of ethylene and acetylene was used to determine how the addition of an adduct molecule affects subsequent additions for coverages up to one molecule per silicon dimer, that is, 100% coverage. Randomization subdues the effect that the relative positions of the adsorbates have on the enthalpy of the system. For ethylene and acetylene, the enthalpy of reaction changes less than 3 and 5 kcal/mol, respectively, from the first reacted species up to 100% coverage. As a result, a (near-)complete coverage is predicted, which is in line with experimental data. When 1-alkenes and 1-alkynes add by [2 + 2] addition, the hydrocarbon chains interact differently depending on the direction they project from the surface. These effects were investigated for four-carbon chains: 1-butene and 1-butyne. As expected, the chains that would otherwise intersect bend to avoid each other, raising the enthalpy of the system. For alkyl chains longer than four carbons, the chains are able to reorient themselves in a favorable manner, thus, resulting in a steady reduction in reaction enthalpy of about 2 kcal/mol for each additional methylene unit.
Grafting of 1-alkynes to hydrogen-terminated (100) silicon surfaces
Applied Physics A: Materials …, 2005
Hydrogen-terminated, atomically flat, 1 × 1 (un)reconstructed, (100)-oriented, silicon surfaces have been functionalized with 1-octyne and then studied via X-ray photoelectron spectroscopy. The C 1s signal shows that the addition of the hydrocarbon chain occurs through the formation of environmentally stable Si−C bonds, in agreement with hydrosilation as the major grafting route.
Functionalization of Acetylene-Terminated Monolayers on Si(100) Surfaces: A Click Chemistry Approach
Langmuir, 2007
In this article, we report the functionalization of alkyne-terminated alkyl monolayers on Si(100) using "click" chemistry, specifically, the Cu(I)-catalyzed Huisgen 1,3-dipolar cycloaddition reaction of azides with surface-bound alkynes. Covalently immobilized, structurally well-defined acetylene-terminated organic monolayers were prepared from a commercially available terminal diyne species using a one-step hydrosilylation procedure. Subsequent derivatization of the alkyne-terminated monolayers in aqueous environments with representative azide species via a selective, reliable, robust cycloaddition process afforded disubstituted surface-bound [1,2,3]-triazole species. Neither activation procedures nor protection/deprotection steps were required, as is the case with more established grafting approaches for silicon surfaces. Detailed characterization using X-ray photoelectron spectroscopy and X-ray reflectometry demonstrated that the surface acetylenes had reacted in moderate to high yield to give surfaces exposing alkyl chains, oligoether anti-fouling moieties, and functionalized aromatic structures. These results demonstrate that click immobilization offers a versatile, experimentally simple, chemically unambiguous modular approach to producing modified silicon surfaces with organic functionality for applications as diverse as biosensors and molecular electronics.
Scientific Reports, 2015
Using two different hydrosilylation methods, low temperature thermal and UV initiation, silicon (111) hydrogenated surfaces were functionalized in presence of an OH-terminated alkyne, a CF 3terminated alkyne and a mixed equimolar ratio of the two alkynes. XPS studies revealed that in the absence of premeditated surface radical through low temperature hydrosilylation, the surface grafting proceeded to form a Si-O-C linkage via nucleophilic reaction through the OH group of the alkyne. This led to a small increase in surface roughness as well as an increase in hydrophobicity and this effect was attributed to the surficial etching of silicon to form nanosize pores (~1-3 nm) by residual water/oxygen as a result of changes to surface polarity from the grafting. Furthermore in the radical-free thermal environment, a mix in equimolar of these two short alkynes can achieve a high contact angle of ~102°, comparable to long alkyl chains grafting reported in literature although surface roughness was relatively mild (rms = ~1 nm). On the other hand, UV initiation on silicon totally reversed the chemical linkages to predominantly Si-C without further compromising the surface roughness, highlighting the importance of surface radicals determining the reactivity of the silicon surface to the selected alkynes.
Journal of the American Chemical Society, 2008
Crystalline Si(111) surfaces have been alkylated in a two-step chlorination/alkylation process using various organic molecules having similar backbones but differing in their C-C bond closest to the silicon surface (i.e., C-C vs CdC vs CtC bonds). X-ray photoelectron spectroscopic (XPS) data show that functionalization of silicon surfaces with propenyl magnesium bromide (CH 3-CHdCH-MgBr) organic molecules gives nearly full coverage of the silicon atop sites, as on methyl-and propynyl-terminated silicon surfaces. Propenyl-terminated silicon surface shows less surface oxidation and is more robust against solvent attacks when compared to methyl-and propynyl-terminated silicon surfaces. We also show a secondary functionalization process of propenyl-terminated silicon surface with 4′-[3-Trifluoromethyl-3Hdiazirin-3-yl]-benzoic acid N-hydroxysuccinimide ester [TDBA-OSu] cross-linker. The Si-CHdCH-CH 3 surfaces thus offer a means of attaching a variety of chemical moieties to a silicon surface through a short linking group, enabling applications in molecular electronics, energy conversion, catalysis, and sensing.
Chemical Physics Letters, 2004
The reaction of the bifunctional organic molecule 1-dimethylamino-2-propyne (DMAP) on the Si(100) surface has been investigated by density functional calculations on a one-dimer cluster model. We found that, once in the physisorbed dative bonded well (À22.1 kcal mol À1), DMAP can proceed to react via a number of pathways. We first considered the cycloaddition of the C"C triple bond, leading to Si-C di-r bonded product (À58.6 kcal mol À1), computing an energy barrier of 33.1 kcal mol À1. We considered also possible dissociative pathways of dative bonded DMAP, i.e., methylene C-H, methyl C-H or N-CH 3 bond cleavage.
Molecular Modeling of Alkyl Monolayers on the Si(111) Surface
Langmuir, 2000
A computational approach has been delineated to model alkyl monolayers on hydrogen-terminated silicon (111) surfaces by molecular mechanics calculations. The monolayers can be properly described by making use of two-dimensionally repeating boxes with minimally ∼30 alkyl chains. For two different substitution patterns on the Si surface, both with an overall substitution percentage of 50%, good agreement between the computational and the available experimental data (FT-IR, X-ray, ellipsometry) was found. It is shown that the thus formed layers are nearly stress-free and that different orientations of individual alkyl chains exist, which combined yield an overall uniformly ordered monolayer.